The proposed work is a multi-faceted project aimed at elucidating the factors that affect gene expression in heterospecific environments. Its specific objectives are: 1) isolation and characterization of transcriptional start signals from selected prokaryotic and eukaryotic sources, 2) investigation of the relationship between the strength of the transcriptional start and the level of expression of structural genes distal to the promoter, 3) use of clones and characterized promoters to express genes in heterospecific environments, 4) investigation of the structural and positional features of ribosomal binding sequences on heterospecific gene expression, 5) study of specific alterations in translational control sites on gene expression, 6) study of the role of intervening sequences of eukaryotic genomic DNA in the production of translational products with this DNA versus corresponding cDNA segments, 7) investigation of the relationship between the location of intervening sequences and the structure of multi-component peptides that are expressed as a single precursor molecule. The proposed work is made possible by recently developed methods for the manipulation of cloning DNA segments and for the detailed analysis of DNA sequence at the nucleotide level.